Alteration of Triassic carbonates in the Buda Mountains —a hydrothermal model

Abstract

Large, irregular volumes of altered, friable Triassic dolomite with poorly recognizable depositional fabrics crop out in the Buda Mountains, Hungary. These rock volumes are characterized by powderlike, chalky, soft, whitish gray microporous carbonates, referred to as "pulverized dolomite". This is interpreted as the result of corrosion of carbonates along microfractures. The pulverized dolomite is commonly associated with silica and clay cementation ("silicification") and "mineralization" of ironrich minerals, barite, sphalerite, galena, fluorite, calcite, dolomite and others, clearly pointing out hydrothermal Mississippi Valley Type (MVT) conditions.The pulverization, silicification and mineralization are considered to be a diagenetic facies association (PSM facies). Tectonic shear corridors played an important role in the development of PSM facies as carriers of hydrothermal fluids, but the geometry of the altered units is very irregular and cross-cuts different Triassic depositional facies in addition to Eocene limestone and MiddleUpper Miocene sediments. The PSM facies represents the early stages of hydrothermal alteration (i.e. the burial phase) that was later modified by thermal mixing zones. Pulverized dolomite bodies that reached the surface were strongly affected by meteoric fluids; peculiar speleo-concretions were formed by calcite cementation of the powdery dolomite clasts.The altered carbonates show major porosity development whereas the unaltered carbonates present only minor porosity. The size and lithologic contrast of the altered geobodies makes them detectable by geophysical methods of mineral and hydrocarbon exploration.

Geothermal reservoir characteristics of Meso- and Cenozoic sedimentary rocks of Budapest (Hungary)

“…Due to the high fracture porosity and the well developed and interconnected fracture system and cavity network in the Buda Hills (Esteban et al 2009), this area is well suited for hydrothermal systems.…”

“…Data from outcrops match the reservoir conditions quite well and thus lead to a conservative estimation of the reservoir utilization. By adding information on secondary porosities (Moench 1984(Moench , Şen 2002, karstification (Esteban et al 2009, Goldscheider et al 2011, and the distinct stress field (Smith & Davies 2006) higher reservoir capacities can be inferred. Additionally, a database including all thermophysical rock properties with each parameter measured on the same samples (Fig.…”

Study on Construction and Reinforcement Technology of Dolomite Sanding Tunnel

“…Liu et al [25] analyzed the vulnerability of sanding soil in Florida to toxic metal pollution and the effectiveness of humic-acid Active Dolomite Phosphate Rock (ADPR) and Biological Carbon (BC) to fixate Cd2+ and Pb2+ in soil restoration. Esteban et al [26] mentioned the influence of hydrothermal action, Machel et al [27] hypothesized that dolomites were dissolved by sulfate during hydrocarbon impregnation, and Poros et al [22] not only induced the above theories but also established a new model of dolomite sanding caused by freeze-thaw process when studying Triassic dolomites in Hungary. Orsolya et al [28] investigated Triassic dolomites in Hungary, selected seven rock-cores for stable isotope analysis, and for identifying the relationship between dolomitization and hydrothermal dissolution.…”

Geothermal reservoir characterization: a thermofacies concept

“…Here, we address the key questions concerning (1) reservoir permeability and (2) thermal conductivity, whereas (3) double porosity (Barenblatt et al. , 1960; Streltsova, 1976; Moench, 1984; Şen, 1988, 2002; Kruseman and De Ridder, 1991), (4) hydrothermal alteration (Browne, 1978) and (5) karstification (Smith and Davies, 2006; Esteban et al. , 2009; Goldscheider et al.…”